This invention is directed to the providing of adequate heat for purposes of a water heater, or other heat utilization device, from an auxiliary standpoint or perhaps enable one to derive a small amount of useful heat for other purposes in the heating of a residential type of building. The source of heat for operation of the system and from which useful heat is obtained for effective transfer to the utilization device by this system is an available heat source but one which would otherwise remain unused. In particular, solar energy is a heat source with which this system is uniquely adapted. A solar powered heating system is normally expected to be supplemented by a gas or electric heating system which provides heat in the event that natural circumstances preclude the operation of the solar system whereas this may not be true with other types of available heat sources. This invention utilizes internal pressures and gravity for effecting the return of a heat transfer medium comprising a volatile fluid that is alternately vaporized and condensed. Additionally, this system includes a valve mechanism which functions as a temperature control for the heat transfer.
Several types of solar heating systems are known. Many have been developed recently in response to the need for additional sources of energy. One recent system developed by Bohanon, U.S. Pat. No. 4,061,131 granted Dec. 6, 1977, relates to a system capable of transferring heat automatically from an evaporator having a heat source of a relatively high temperature to a condenser associated with a heat sink of a lower temperature and at an elevation below that of its source without the necessity of using an external source of energy to return condensed liquid to the evaporator. Even with its advantages, Bohanon possesses some disadvantages. First, there is no temperature control. Fluid transfer in Bohanon's system is continuously maintained based on the level of fluid in the transfer tank. When enough fluid has accumulated in the transfer tank the drain valve is opened to permit liquid transfer into the evaporator. Regardless of the system temperature or whether the heat sink has reached its desired temperature, Bohanon continues to function allowing liquified fluid to continue to be returned to accumulate in the transfer tank and from which it continues to be periodically returned to the evaporator. Thus Bohanon's system continued to generate heat which is transferred to the heat sink regardless of its heat requirements.
Secondly, the transfer tank of Bohanon must be cooler than the heat sink to permit the system to effect liquid flow into the transfer tank. When the ambient temperature is close to or higher than the sink temperature, the Bohanon system will not function as the vapor pressure in the transfer tank will resist liquid flow. Therefore, when the system operates, either some transferred heat must be dissipated and lost in the process or the fact must be accepted that the system will be unable to function until the ambient temperature drops below that of the transfer tank. In direct contrast, the system of this present invention will deliver liquid to its accumulator regardless of the ambinet temperature or the minimum heat sink temperature. No heat, other than normal heat loss, is expended to facilitate operation of the system. In eliminating these two major disadvantages, the heat transfer system of this invention works better over a wider range of temperatures than Bohanon. This self return system possesses improved efficiency since a greater percentage of heat is actually transferred through the system.
Other known examples of heating systems of the type to which this invention is directed are illustrated in U.S. Pat. No. 2,210,511 issued to R. S. Taylor, U.S. Pat. No. 3,390,672 issued to C. D. Snelling, U.S. Pat. No. 3,991,938 issued to H. B. Ramcy and U.S. Pat. No. 4,007,776 issued to K. A. Alkasab. These patents, while illustrative of other heating systems having a self-contained liquid return feature, do not disclose apparatus possessing the advantages and improved functioning of the heat transfer system of this invention.